1. Field of the Invention
The present invention relates to an image formation apparatus configured to be capable of providing a silk-textured image by forming desired irregularities on a surface of a thermal transfer receiving sheet, and a method for forming an image in which a silk-textured image can be provided by forming desired irregularities on a surface of a thermal transfer receiving sheet.
2. Description of the Related Art
A sublimation-type thermal ink-transfer recording technique is an image formation technique that is neither a silver-salt photographic process nor an electrophotographic process and provides images similar to silver-salt color photographic images in an instant with compact equipment that is easily maintained. The principle of this type of image formation is as follows: thermal energy that is controlled in accordance with image signals is provided to a thermal head, color materials on a thermal transfer sheet are phase-changed (becoming molten or sublimed) as a result of the thermal energy and transferred onto a recording sheet, thereby forming an image with gradation. Such a recording technique uses, as color materials, dyes that are extremely sharp and highly transparent. For this reason, use of such a recording technique can provide images that are excellent in terms of the reproducibility of halftones and gradation properties and have a quality equivalent to that of silver-salt photographic images.
With the recent trend toward widespread use of computers in individual households, various recording techniques such as a sublimation-type thermal ink-transfer recording technique and an inkjet recording technique have been markedly applied to home use. With the recent trend toward remarkable proliferation of digital cameras, there is an ever increasing demand for photographic printing that provides high image quality equivalent to that of silver-salt photographic images.
Among various features demanded for photographic printing, one feature is providing of silk-textured images. Silk-textured images provided by a silver-salt photographic process are formed so as to have micro irregularities on their surfaces, thereby causing scattering of light and reducing specular reflection. Silk-textured images maintain the micro gloss on their surfaces while having reduced image clarity, thereby providing a quality appearance. Formation of silk-textured images is an advantageous technique for adding a quality appearance to large photographic images, in particular, portrait-size images. Such formation of silk-textured images is also demanded in a sublimation-type thermal ink-transfer recording technique.
Japanese Unexamined Patent Application Publication No. 2006-182012 discloses a method for forming a printed matter by overlapping a thermal transfer image receiving sheet including a substrate and a receiving layer on the substrate and a thermal transfer sheet including a substrate and a dye layer containing a sublimation dye on the substrate, and heating the overlapped sheets. Specifically, a thermally transferred image is formed on the receiving layer with the sublimation dye and a protective layer is subsequently thermally transferred onto at least a portion of the thermally transferred image with a thermal transfer sheet including a substrate and the protective layer that can be thermally transferred on the substrate. Japanese Unexamined Patent Application Publication No. 2006-182012 also proposes a method for forming a printed matter, a surface of which is matted under a heating condition by stamping at least one portion of the protective layer with an embossed plate having irregularities on its surface. However, such a method for forming a printed matter according to Japanese Unexamined Patent Application Publication No. 2006-182012 is conducted with an extra large apparatus together with a printer, thereby adding extra costs. Such a method is also conducted with an extra step together with printing steps with a printer, thereby reducing productivity.
Japanese Unexamined Patent Application Publication No. 2000-153674 discloses a pigment-donor element for thermal pigment transfer, the element including, on a substrate, at least one pigment-layer region containing image pigment in a binder and a region constituting a protective layer that can be transferred. Specifically, the size of the region constituting a protective layer that can be transferred is substantially the same as the size of the pigment-layer region. The protective layer contains unexpanded synthetic thermoplastic polymer microspheres and the diameter of the microspheres in the unexpanded state is in the range of 5 to 20 μm. Japanese Unexamined Patent Application Publication No. 2000-153674 proposes that the microspheres are expanded to a diameter in the range of 20 to 120 μm upon heating in transferring the protective layer onto an image receiving layer for the purpose of adding a matte surface to the surface of the image receiving layer. However, use of the method disclosed in Japanese Unexamined Patent Application Publication No. 2000-153674 does not provide surface irregularities for forming silk-textured images and a silk texture equivalent to that of silver-salt photographic images is not provided. Additionally, since the protective layer contains microspheres, use of the method disclosed in Japanese Unexamined Patent Application Publication No. 2000-153674 provides matte surfaces and hence switching between formation of gloss images and formation of silk-textured images in accordance with demand is not conducted.
Japanese Unexamined Patent Application Publication No. 2004-106260 discloses a method for forming a protective layer in which a protective layer is thermally transferred onto an image on a receiver with a protective-layer transfer sheet, and the gloss of the surface of the protective layer can be changed by controlling the degree of heating upon the thermal transfer. In the protective-layer transfer sheet, the protective layer composed of a thermoplastic resin and an inorganic layer compound and an adhesion layer that can be thermally transferred are sequentially stacked on a substrate. However, use of the method disclosed in Japanese Unexamined Patent Application Publication No. 2004-106260 only provides variation in the gloss of the surface of the protective layer and does not provide irregularities on the surface for forming silk-textured images. Thus, a silk texture equivalent to that of silver-salt photographic images is not provided.
Japanese Unexamined Patent Application Publication No. 2007-076332 discloses that, when variation Dx in the thickness of a recording medium upon thermal transfer of the color material layer of a thermal transfer sheet onto the recording medium is defined by the following formula (1), and variation Dy in the thickness of the recording medium upon thermal transfer of the protective layer of a thermal transfer sheet onto the thermally transferred image on the recording medium is defined by the following formula (2), the carrying speed of the recording medium is controlled such that Dy≧Dx is satisfied.Dx=|Lb−La| . . .   (1)Dy=|Lc−La| . . .   (2)
La=thickness of recording medium before image formation
Lb=thickness of recording medium at position having minimum thickness after image formation
Lc=thickness of recording medium in the case of applying, to thermal head, minimum thermal energy capable of thermally transferring protective layer onto recording medium
Specifically, Japanese Unexamined Patent Application Publication No. 2007-076332 proposes that surface irregularities for providing silk-textured images are formed by increasing the carrying speed of the recording medium upon thermal transfer of the color material layer thereby to reduce the degree of collapse of the recording medium in the thickness direction upon the thermal transfer of the color material layer, and by decreasing the carrying speed of the recording medium upon thermal transfer of the protective layer thereby to increase the degree of collapse of the recording medium in the thickness direction upon the thermal transfer of the protective layer. However, in this case, since the recording medium is collapsed in the thickness direction upon the thermal transfer of the color material layer, there is a possibility that a sufficiently large collapse margin for forming irregularities having a large height difference for providing a silk texture equivalent to that of silver-salt photographic images is not provided upon the thermal transfer of the protective layer.